1. Field of the Invention
The present invention relates to an optical disc drive that can write information on an optical disc.
2. Description of the Related Art
In optical disc technologies, data can be read out from a rotating optical disc by irradiating the disc with a relatively weak light beam with a constant intensity and detecting the light that has been modulated by, and reflected from, the optical disc. On a read-only optical disc, information is already stored as pre-pits that are arranged either concentrically or spirally during the manufacturing process of the optical disc. On the other hand, on a rewritable optical disc, a recording material film, from/on which data can be read and written optically, is deposited by evaporation process, for example, on the surface of a substrate on which concentric or spiral grooves are arranged. In writing data on a rewritable optical disc, data is written there by irradiating the optical disc with a pulsed light beam, of which the optical power has been changed according to the data to be written, and locally changing the property of the recording material film.
In a recordable or rewritable optical disc, when data is going to be written on its recording material film, the recording material film is irradiated with such a light beam, of which the optical power has been modulated as described above, thereby recording an amorphous mark on a crystalline recording material film. Such an amorphous recorded mark is left there by heating a portion of the recording material film that has been irradiated with a writing light beam to a temperature that is equal to or higher than its melting point and then rapidly cooling that portion. If the optical power of a light beam that irradiates the recorded mark is set to be relatively low, the temperature of the recorded mark being irradiated with the light beam does not exceed its melting point and the recorded mark will turn crystalline again after having been cooled rapidly (i.e., the recorded mark will be erased). In this manner, the recorded mark can be rewritten over and over again. However, if the optical power of the light beam for writing data (i.e., optical recording power) had an inappropriate level, then the recorded mark would have a deformed shape and sometimes it could be difficult to read the data as intended.
To read data that is stored on an optical disc or to write data on a rewritable optical disc, the light beam always needs to maintain a predetermined converging state on a target track. For that purpose, a “focus control” and a “tracking control” need to be done. The “focus control” means controlling the position of an objective lens along a normal to the surface of the optical disc (such a direction will sometimes be referred to herein as “optical disc depth direction”) so that the focal point (or at least the converging point) of the light beam is always located on the target track. On the other hand, the “tracking control” means controlling the position of the objective lens along the radius of a given optical disc (which direction will be referred to herein as a “disc radial direction”) so that the light beam spot is always located right on the target track.
In order to perform such a focus control or a tracking control, the focus error or the tracking error needs to be detected based on the light that has been reflected from the optical disc and the position of the light beam spot needs to be adjusted so as to reduce the error as much as possible. The magnitudes of the focus error and the tracking error are respectively represented by a “focus error (FE) signal” and a “tracking error (TE) signal”, both of which are generated based on the light that has been reflected from the optical disc.
Japanese Patent Application Laid-Open Publication No. 5-109206 (which will be referred to herein as “Patent Document No. 1”) discloses a technique for reducing the need for re-recording, which would be troublesome for the user, by eliminating as much as possible the lack of information that should have been written on an optical disc.
However, Patent Document No. 1 pays no attention to the fact that if the optical disc were irradiated with a light beam with too low intensity or rotated with too high velocity, then the mark recorded would not represent the intended information exactly (i.e., would have poor recording quality).
It is therefore an object of the present invention to provide an optical disc drive that can improve the quality of a mark that has been recorded on an optical disc.